The present invention relates to an apparatus for recognizing a logical status change in one or more channels of an n-bit multiplex signal, especially in signaling (DS) devices.
As described in "Pflichtenheft fuer Fehler und Stoerungssignalisierung fuer PCM- und DS-Geraete" of the German Federal Mails, Central Telecommunications Office, Department N12, FTZ 153 Pfl . . . , Second Edition, several important functions of a system are monitored with the assistance of special monitoring circuits incorporated in the system devices. When such a monitoring circuit indicates an error or other condition, then an indicator in the form of a LED is lit in the device recognizing the error, and an error report is transmitted. Generally, error reports of a plurality of devices are grouped together, and the error reports of such devices are connected onto common lines.
The levels of significance of an error alarm is distinguished on the basis of priority, or the urgency of the error type. An A type error or urgent alarm, must be immediately handled, even outside of regular working hours, for example during nights and holidays. A B type or non-urgent alarm can be handled during regular working hours. At the individual devices, the error reports are switched on to different signal lines by means of switching bridges. As long as the error condition remains, the LED is lit in the device, and a grounded potential is applied to the signal line AZ (for type A-alarms) or BZ (for type B-alarms). The begining of the error condition is also reported by sending a pulse onto a signal line A or B, which results in the excitation of an alarm lamp A or B. The alarm condition is also forwarded via alarm lines to another indicator device and an alarm lamp A or B is also illuminated there.
The alarm report can be disconnected by manually pressing an acknowledgment key. This causes a reminder alarm lamp EL in the signal field, and in the light display means, to be lit, instead of the alarm lamps A or B. The reminder alarm lamp EL can also light up when a switch or plug in the device is not in its operational condition.
The alarm outputs A and B, and the reminder lamps EL, of a given group of error reports and the alarm outputs of all light display means are combined to form a single collective error signal. This collective error signal is then forwarded to a central place of operational supervision, and signifies only that some system part in an operating location has produced an error report. The reminder lamp in the signal field and the light display means are: lluminated as long as an error report is being produced from a device, so that one of the status lines AZ or BZ remains grounded as long as the error report continues. In addition, as long as the switch or plug is not in its operational condition the reminder lamp EL also remains energized.
In multiplex devices, it is desirable that each input be able to produce a new error report independently of the other inputs for an error report, for example, the disconnection of an normal input signal, even when there is already an error report of an input which has been acknowledged. That is, a pulse must be produced on the bus line A or B whenever another error occurs, even when the status line (AZ or BZ) is still activated.
In a previously proposed system, an input of an OR gate is provided for connection to receive error reports from each channel, and the output of this OR gate is directly connected to the signal line AZ or BZ, and through a pulse shaper to the signal line A or B. While this results in a reporting of the first error to occur, subsequent errors are hidden by the operated condition of the OR gate.